INTERFERON-ALPHA SELECTIVELY ACTIVATES THE BETA-ISOFORM OF PROTEIN-KINASE-C THROUGH PHOSPHATIDYLCHOLINE HYDROLYSIS

The early events that occur after interferon binds to discrete cell surface receptors remain largely unknown. Human leukocyte interferon (interferon-α) rapidly increases the binding of [3H]phorbol dibutyrate to intact HeLa cells (ED50 = 100 units/ml), a measure of protein kinase C activation, and induces the selective translocation of the β isoform of protein kinase C from the cytosol to the particulate fraction of HeLa cells. The subcellular distribution of the α and ε isoforms is unaffected by interferon-α treatment. Activation of protein kinase C by phorbol esters mimics the inhibitory action of interferon-α on HeLa cell proliferation and down-regulation of protein kinase C blocks the induction of antiviral activity by interferon-α in HeLa cells. Increased phosphatidylcholine hydrolysis and phosphorylcholine production is accompanied by diacylglycerol production in response to interferon. However, inositol phospholipid turnover and free intracellular calcium concentration are unaffected. These results suggest that the transient increase in diacylglycerol, resulting from phosphatidylcholine hydrolysis, may selectively activate the β isoform of protein kinase C. Moreover, the activation of protein kinase C is a necessary element in interferon action on cells.